Sony MDR-IF240RK Wireless Headphone System Connectivity Technology: Wireless IR wireless system with 24-foot range and 90 degree maximum transmission angle NiCad battery lasts up to 30 hours on a single charge, recharges in 24 hours Headphones feature 30mm diameter PET drivers with ferrite magnet for superb sound Lightweight (6.3 ounce) phones feature open-air design with wide headband for comfort Frequency response: 18Hz - 22,000Hz